Rishi Gupta

Electrical Resistivity of Concrete for Durability Evaluation: A Review

Degradation processes in reinforced concrete structures that affect durability are partially controlled by transport of aggressive ions through the concrete microstructure. Ions are charged and the ability of concrete to hold out against transfer of ions greatly relies on its electrical resistivity. Hence, a connection could be expected between electrical resistivity of concrete and the deterioration processes such as increase in permeability and corrosion of embedded steel. Through this paper, an extensive literature review has been done to address relationship between concrete electrical resistivity and its certain durability characteristics. These durability characteristics include chloride diffusivity and corrosion of reinforcement as these have major influence on concrete degradation process. Overall, there exists an inverse or direct proportional correlation between these parameters. Evaluated results, from measuring the concrete electrical resistivity, can also be used as a great indicator to identify early age characteristics of fresh concrete and for evaluation of its properties, determination of moisture content, connectivity of the micropores, and even condition assessment of in-service structures. This paper also reviews and assesses research concerning the influential parameters such as environmental conditions and presence of steel rebar and cracks on measuring electrical resistivity of concrete. Moreover, concrete resistivity concept, application, and its various measurement techniques are introduced.

Innovative Test Technique to Evaluate "Self-Sealing" of Concrete

Concrete is prone to cracking when subjected to tensile forces because of its low tensile strength. The cracking potential is an even bigger concern when concrete is relatively young and is in the plastic stage. Cracks induced early can grow with time because of drying shrinkage and with application of service loads. Concrete, which is otherwise impermeable, allows for free passage of moisture and other deleterious chemicals when it is cracked, leading to reduced durability of the material and, in many cases, reduced service life of the structure. The severity of some of these issues can be alleviated because of an inherent property of concrete known as “self-sealing.” As the name suggests, “self-sealing” allows for the cracks (of limited width) to be sealed on their own over a period of time. However, currently there is no standard test technique to quantify this property of concrete and other cement-based materials, such as mortar. An innovative and straightforward technique was developed by the authors and is presented in this paper. In this technique, a standard crack is induced in concrete cylinders using a standard crack-inducing jig (SCIJ). The specimens are then inserted in special rubber sleeves and this assembly is then subjected to a constant water head. The reduction in flow through the cracked specimen is measured at a given time to compare the performance of different specimens. This technique can also be used to compare the performance of concrete mixes modified using various admixtures. This paper describes this innovative test technique and includes sample test results to explain the analysis process proposed by the authors.

Do crystalline water proofing admixtures affect restrained plastic shrinkage behavior of concrete

This paper describes the effect of crystalline water proofing admixtures on early-age cracking in concrete. The performance of three different types of these admixtures was compared to that of control. This study has been performed in two stages. Stage one was performed under ASTM specified conditions and a modified stage where more severe drying conditions than that described in the ASTM test standard were used. These modified conditions simulated inadequate curing under extreme exposure conditions as experienced by concrete in many parts of the world. The test results indicate that the water proofing admixtures can effectively reduce the early-age shrinkage cracking. The possible reasons for this secondary advantage of crystalline water proofing admixture is also hypothesized in this paper.

Unmanned aerial vehicle-based sounding of subsurface concrete defects

A sounding technique that uses an unmanned aerial vehicle (UAV) equipped with two microphones can detect subsurface concrete defects. Use of flexural vibration frequency as a basis for defect depth estimation is evaluated. While many non-destructive tests for concrete can detect depth, current UAV-based inspection methods like optical and thermal imaging are typically limited to two-dimensional subsurface defect information. Acoustic signals from sounding and UAV noise are known to exist in similar frequency ranges. Accordingly, three noise reduction measures for this sounding technique are assessed. Given adequate distance between the microphones and UAV, a two microphone signal subtraction technique is slightly effective for some noise, but a spectral noise gating procedure is shown to substantially decrease noise in the frequency range of interest.

Minor defect correlation with dynamic elastic properties of polypropylene fiber-reinforced concrete

Efficient rehabilitation of aging civil infrastructure requires innovative and emerging materials along with proper implementation of Structural Health Monitoring (SHM). Prior to identifying a strategic SHM technique, understanding of defects in structures is vital. Common defects in concrete include consolidation problems and development of micro-cracks during consolidation or stress induction. Monitoring the dynamic characteristics of concrete can play an essential role in detecting real-time and early stages of deterioration. Much research is focused on detecting large defects; however, not much information is available on detection of minor defects in composites like Fiber Reinforced Concrete (FRC). This study focuses on testing and monitoring the dynamic elastic behavior of concrete using a non-destructive resonant frequency approach. The change in dynamic elastic properties of normal concrete under flexural and compression loading is analyzed. Moreover, an initial attempt to monitor the change in el...

Fiber-Reinforced Cement Composites: Mechanical Properties and Structural Implications

Department of Architectural Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea Department of Civil Engineering, (e University of British Columbia, 6250 Applied Science Lane, Vancouver, BC V6T 1Z4, Canada Department of Civil and Environmental Engineering, National Defense Academy, Yokosuka 239 8686, Japan Department of Civil and Environmental Engineering, University of Louisville, Louisville, KY 40292, USA Department of Civil Engineering, University of Victoria, 3800 Finnerty Road, Victoria, BC V8W 2Y2, Canada

Advanced Cementitious Materials: Mechanical Behavior, Durability, and Volume Stability

1Department of Architectural Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea 2Department of Civil Engineering, The University of British Columbia, 6250 Applied Science Lane, Vancouver, BC, Canada V6T 1Z4 3Department of Civil and Environmental Engineering, National Defense Academy, Yokosuka 239 8686, Japan 4Department of Civil Engineering, Federal Centre for Technological Education of Minas Gerais (CEFET-MG), Av. Amazonas 7675, 30510-000 Belo Horizonte, MG, Brazil 5Department of Civil Engineering, University of Victoria, 3800 Finnerty Road, Victoria, BC, Canada V8W 2Y2

Effect of Formwork, Wall Thickness, and Addition of Fly Ash on Concrete Hydration

The writers thank Octaform Systems Inc. for sponsoring this project and for providing the materials and technical expertise for this project. The writers also acknowledge the contributions of the Seattle University senior design team comprising Kristian Lowrie, David Sommer, and Nikki Wheeler.